Heat exchanger defrost apparatus

ABSTRACT

A plate and tube heat exchanger assembly includes a plurality of coolant transporting tubes and a plurality of spaced plates to be periodically defrosted. The tubes pass through the plates and are in heat conducting relationship therewith at junction points with the plates. At least one but less than all of the plates may be modified, according to the instant invention, to include an electric heating element disposed at one end thereof for imparting heat through the plate and to the tubes and other plates at the junction points therebetween at predetermined times for periodic defrosting. The thickness of the plates having heating elements associated therewith are of a greater thickness than the remainder of the plates.

United States Patent Seipp et a1. 7

I HEAT EXCHANGER DEF ROST APPARATUS [75] Inventors: Ronald W. Seipp,Rosemont; Harold E. McClure, Wayzota, both of Minn.

[73] Assignee: Thermo King Corporation,

Minneapolis, Minn.

22 Filed: Nov. 15, 1972 211 Appl. No.: 306,665

[52] US. Cl 219/201, 62/276, 219/365,

. .219/530, 219/540 [51] Int. Cl H05b l/0.0, F25d 21/00 [58] Field ofSearch"... 62/80, 82, 148, 151, 6,2/275-277; 219/341, 365, 530, 540,200, 201

[56] References Cited I I I UNITED STATES PATENTS 2,529,215 11/1950Hicke 62/276X 3,099,914 8/1963 Dewitt et a1. 62/276 3,358,467 12/1967Hickox et a1. 62/80 X 1,073,813 9/1913 Neiman 219/365 UX 2,492,39712/1949 Peterson 62/276 1 Jan. 15, 1974 3,138,006 6/1964 Moorman et a1.62/276 X FOREIGN PATENTS OR APPLICATIONS 1,127,062 4/1962 Germany219/540 Primary Examiner-A. Bartis Att0rneyF. H. Henson et a1.

[57] v i ABSTRACT A plate and tube heat exchanger assembly includes aplurality of coolant transporting tubes and a plurality of spaced platesto be periodically defrosted. The tubes pass through the plates and arein heat conducting relationship therewith at junction points with theplates. At least one but less than all of the plates may 1 be modified,according to the instant invention, to include an electric heatingelement disposed at one end thereof for imparting'heat through the plateand to the tubes and other plates at the junction points therebetween atpredetermined times for periodic defrosting. The thickness of the plateshaving heating elements associated therewith are of a greater thicknessthan the remainder of the plates.

4 Claims, 3 Drawing Figures HEAT EXCHANGER DEFROST APPARATUS BACKGROUNDOF THE INVENTION will be transmitted by conduction to the heat transferv surfaces of the evaporator to melt accumulated frost and ice build-up.However, these. present attempts have been partially unsuccessful inthat the heating elements may be inaccessible or may cause substantialdamage if a moisture leak were to cause the heater to explode.

Therefore, it would be desirable to provide an improved apparatus forattaching heating elements to a PRIOR ART Reference may be made to thefollowing U.S. Patent which generally shows defrost apparatus for arefrigeration heat exchanger and evaporator coil including a clampingassembly for retaining an electric heating element to the evaporatorcoil:

U.S. Pat. No. 2,930,207, L. H. Carl et a1, Mar. 29,

1960. However, no patents are known which disclose a heat exchangerincluding at least one extending heat exchanger plate having arespective means for importing heat through the plate and to the tubingat junction points therebetween.

SUMMARY OF THE INVENTION This invention relates to a plate and tube heatexchanger assembly, such as that comprising a refrigerator evaporator,which includes a plurality of parallel coolant transporting tubes and aplurality of spaced plates which are to be periodically defrosted. Theplates extend transversely from the tubes, and the tubes are adapted topass through and be in heat conducting. relationship with the plates atjunction points with the plates. At least one of the plates has arespective heating element disposed at one end. In the preferred form,the heating element is a tubular electrical heating device which isretained at the end of a respective plate by means of a clamp in orderthat heat generated by the device may be imparted to the plate andthrough the tubes to other plates at the junction points therebetween ata predetermined time when it is desired to accomplish the periodicdefrosting.

A respective plate having a heating element attached thereto may bemodified in accordance with the inven-' tion to include a transverselyextending leg. The leg extends below the tubes and is adapted to securethe plate to the assembly defrost and collection pan in order that heatmay be supplied thereto in the assembled relationship to insure freedraining.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top plan view of the heatexchanger and evaporator section of a refrigeration system employing thedefrost apparatus of the present invention;

FIG. 2 is a frontal elevation of the heat exchanger section assembled inrelation to the refrigeration system defrost and collection pan; and

FIG. 3 is an isometric view of one of the heat ex.- change platesmodified in accordance with the instant invention to include a tubularelectric heating element.

DESCRIPTION OF THE PREFERRED EMBODIMENT Relating to FIGS. 1 and 2 of thedrawings, a well known plate and tube heat exchange assembly 1 is shown.Assembly 1 comprises a plurality of generally parallel coolanttransporting tube segments 2 and a plurality of thermally conductivespaced plates or thin fin members 4 which extend transversely from thetubes. Tubes 2 may be serially connected together and disposed in thegeneral configuration of a coil 35 with a coolant inlet end 7 and acoolant outlet end 8 by connecting U-shaped end members 6 to tubes 2 asillustrated, or in any other suitable fashion. In the preferredembodiment, heat exchanger assembly 1 is an air cooling evaporator withthe connected tube configuration representing the evaporator coil 35.The evaporator assembly 1 also includes conventional transverse framemembers 10 and a defrost and collection pan 12, The evaporator coil 35is adapted to make a series of passes through apertures 25 (best shownin FIG. 3) provided in the fin members. The tube segments 2 are in heatconducting relationship with the junction points formed with the fins.

It is well known that heat exchanger assemblies of the present typerequire periodic defrosting to prevent the buildup of frost on the finmembers 4 which could impede the flow of air therethroughandconsequently reduce the cooling effectiveness of the unit. An improveddefrost apparatus has been developed which may successfully transmitheat into the evaporator coil to prevent front accumulation among thefin members, as will be detailed more fully hereinafter.

In accordance with the instant invention, individual fin members atregularly spaced intervals may be replaced by a modified thick plate 15which is fabricated from a highly heat conductive material, such asAluminum, for example. The thickness of plates 15 may be equal to aboutten times the regular thickness of fin members 4. Each plate 15 includesa heating element for defrosting the evaporator and a means forretaining the heating element to the plate. Although, as illus-' trated,the heating element is disposed at one end of the plates 15, it iswithin the scope of this invention to retain a heating element from bothends of the plates simultaneously. In the preferred embodiment, theheating element is a tubular electric heater 20 such as those knownunder the trade names of Calrod or Corox, but any other conventionaltubular heater may be employed equally well.

As best illustrated in FIG. 3, the heater element is attached to theplate 15 by means of a clamp 22. The clamp 22 may comprise complementaryhalves 23 and 24 fastened together by any suitable means, such as bybolt 27 with the tubular electric heater 20 interposed between thehalves, as shown, or, the clamp may be a single, uniform member.

The defrost apparatus just described may provide a more even thermaldistribution across the heat exchanger evaporator coil 35 and defrostmore effec tively than conventional methods of imbedding tubular heaterswithin the edgeof the coil. With the present defrost apparatus, thethick highly heat conductive plates can provide a rigid heater retentionmeans while acting asa primary conduction path for imparting heatthrough the plate to the tube segments 2 at the junction pointstherebetween. The heat may then be evenly distributed through theevaporator coil and to the thin fin members 4 at predetermined times forperiodic defrosting of the fins when any suitable switch means (notshown), connected in line between an electric power source (not shown)and a respective heater, is manually or automatically turned on toprovide the heating element with a current supply.

Heat conducting plates 15 may be further modified as shown in FIG. 3, toinclude a foot member 30 extending transversely from the plate. As bestshown in FIG. 2, foot 30 extends below the evaporator coil 35 to adaptplates 15 to rest upon and be secured to the evaporator defrost andcollection pan 12 in the assembled relationship. The tubular heaters maytherefore provide a direct source of heat for the collection pan 12 topermit the pan to be freely drained.

A defrost apparatus has been disclosed which not only provides for auniform heat distribution and effi cient defrosting of the evaporatorheat exchange fins but is also a source of heat for the defrost andcollecplacement. Other modifications will occur to those skilled in theart.

We claim:

1. A plate tube heat exchanger assembly including a plurality ofparallel coolant transporting tubes and a plurality of spaced plates tobe periodically defrosted and extending transversely from said tubes,said tubes passing through said plates and being in heat conductingrelationship therewith at junction points with said plates, 2. selectnumber of said parallel plates comprising less than all of saidplurality of spaced plates having respective heat imparting meansconnected thereto, the thickness of each of said select number of platesbeing greater than the relative thickness of the remainder of the platesnot having said heat imparting means, whereby heat is transferredthrough said select number of plates of increased thickness and to saidtubes at the junction points therebetween at predetermined times forperiodic defrosting.

2. The invention of claim 1, wherein the means for imparting heat is atubular electric heater.

3. The invention of claim 1, wherein said heat imparting means isdisposed at one end of said respective plates by a clamp.

4. The invention of claim 1, wherein said plates having respective heatimparting means include a foot member extending transversely from saidplates to adapt said plates to be secured to a heat exchanger defrostand collection pan.

1. A plate tube heat exchanger assembly including a plurality ofparallel coolant transporting tubes and a plurality of spaced plates tobe periodically defrosted and extending transversely from said tubes,said tubes passing through said plates and being in heat conductingrelationship therewith at junction points with said plates, a selectnumber of said parallel plates comprising less than all of saidplurality of spaced plates having respective heat imparting meansconnected thereto, the thickness of each of said select number of platesbeing greater than the relative thickness of the remainder of the platesnot having said heat imparting means, whereby heat is transferredthrough said select number of plates of increased thickness and to saidtubes at the junction points therebetween at predetermined times forperiodic defrosting.
 2. The invention of claim 1, wherein the means forimparting heat is a tubular electric heater.
 3. The invention of claim1, wherein said heat imparting means is disposed at one end of saidrespective plates by a clamp.
 4. The invention of claim 1, wherein saidplates having respective heat imparting means include a foot memberextending transversely from said plates to adapt said plates to besecured to a heat exchanger defrost and collection pan.